Add relative jump support to goto functionality

[9init]

Add relative jump support to goto functionality

This PR adds support for relative jumps in hexedit's goto feature (Ctrl+G, F4, Enter). Users can now specify relative offsets using + or - prefixes to jump forward or backward from the current position.

Changes Made

• Added parsing for + and - prefixes to detect relative jumps
• Implemented relative position calculation based on current cursor position (base + cursor)
• Added underflow protection (negative results are clamped to position 0)
• Maintains full backward compatibility with absolute addresses

Usage Examples

• +0x12 - Jump forward 18 bytes (0x12 = 18 decimal)
• -0x12 - Jump backward 18 bytes
• +100 - Jump forward 100 bytes
• -50 - Jump backward 50 bytes
• 0x200 - Jump to absolute position 0x200 (existing functionality preserved)